y. "If you'll do that I'll stay here and
rest. Afternoon will do for me to go out. Now mind, Flossie and Freddie,
don't get lost again!"

The small twins promised they would not and soon all four were on their
way downtown with their father. This time they went in the subway, or
underground road, which, as Freddie said, was like one big, long tunnel.

"We'll get out at the Brooklyn Bridge or City Hall Park," said Mr.
Bobbsey. "I have to see a man in the City Hall, and from there we can walk
to the Battery, as it is a nice day. Or we can ride, if you get too
tired."

The children were sure they would not get too tired, and a little later
they all got out at the subway station at Brooklyn Bridge.

There were many persons hurrying to and fro, trains coming in and going
out, and lights all over, making the children think it was night, though
it was in the morning.

"Wait here just a minute," said Mr. Bobbsey, showing the twins a less
crowded place where they could stay. "I want to get a magazine over at the
news-stand," he added.

The magazine he wanted had been put away under a pile of papers, and as
the boy was getting it out Flossie caught sight, down the platform, of a
man pasting up on the advertising boards in the underground station, some
new posters.

"Oh, maybe it's signs about a circus, Freddie!" cried the little girl
"Come on and watch!"

Freddie was always ready to go, and he had darted off after his sister
down the long platform before Bert and Nan saw them. When the two older
children missed the younger twins they looked hurriedly about for them.

"There they are--watching that bill-poster," said Bert. For the
underground subway stations are much used by advertisers, gaily colored
sheets of paper being pasted on boards put there for that purpose.

"You mustn't run away like that!" said Nan to Flossie, as she came up to
her sister, to lead her back.

"We wanted to see if it was a circus poster, but it isn't," returned
Freddie.

"Well, come on back. Daddy will miss us," declared Bert. He started
back--at least he thought he did--for the place where their father had
told them to wait for him. But the subway station under the New York
sidewalks was so large and rambling, there were so many stairways leading
here and there, up and down, and there were so many platforms that it is
no wonder Bert went astray.

"Where are you going?" asked Nan at last.

"Well, I was trying to find the place father to